This invention relates to suction catheter assemblies and valves.
The invention is more particularly concerned with medical suction catheter assemblies including valves which can be used for aspirating secretions from tracheal tubes or, for example, for removing blood and debris from surgical sites.
Suction catheter assemblies of this kind are connected to the inlet of a container, the outlet of the container being connected to a vacuum pump so that a reduced pressure is created in the container which in turn applies suction to the catheter. In such systems, the vacuum pump generally operates continuously and the catheter includes a valve by which suction at the tip of the catheter can be controlled. In its simplest form, the valve comprises an aperture in the wall of the catheter which, when open, allows air to enter the catheter and thereby prevents any significant suction effect at the tip. The aperture can be closed, when desired, by the thumb of the user, or by a movable flap, so that the suction effect is confined to the tip of the catheter.
Examples of such catheters are described in U.S. Pat. No. 3,911,919 and U.S. Pat. No. 4,468,216. The problem with this form of valve is that the suction control aperture provides a path through which contaminated material sucked into the catheter can leak out. This is a significant disadvantage in view of the present concern about cross-infection and the transmission of infectious diseases.
In order to reduce the risk of escape of material, catheters have been made which include a sealed valve. Examples of suction catheters with a push-down spool valve are shown in U.S. Pat. No. 4,680,026, U.S. Pat. No. 4,526,573 and U.S. Pat. No. 4,502,508. A suction catheter with a resilient valve member is described in U.S. Pat. No. 4,569,344. Many other forms of suction catheter with different suction control valves are also known.
One problem with these valves is that they have as a part of their sealing system an obstruction to flow. The obstruction is created by the stem which connects the spool, plunger or other seal to the manually-actuable button by which the valve is operated. In some valves the stem itself creates the seal. The obstruction created by the stem causes the fluid flow path to be split into two paths around opposite sides of the stem. This does not permit the free flow of thick fluids, such as thick respiratory fluids.